In a muddy water-shield process, reverse process, or other general civil engineering works, inhalation and compression-transport of muddy water, sand or sludge are required. Therefore, a hose used for such applications should light-weigh and should have flexibility, and it requires excellent abrasion resistance in addition to superior pressure proof.
Thus, a composite hose has been proposed, which is formed from a synthetic resin material with light weight and excellent flexibility and a rubber material having superior pressure proof and abrasion resistance. By way of illustration, Japanese Patent Publication No. 52317/1984 (JP-B-59-52317) proposes a flexible hose as produced by adhering an outer layer and an inner layer to form a composite, in which the outer layer is formed by spiraling a soft resin strip embedded with a hard reinforcement, and the inner layer is formed by winding a rubber strip in a spiral form. Such flexible hose is available on the market. The literature refers to a hard poly(vinyl chloride) as the hard resin of the reinforcement, and a soft poly(vinyl chloride) as the soft resin of the strip. It also mentions that a polysulfide rubber is preferred as the rubber constituting the inner layer.
The polysulfide rubber has, however, poor abrasion resistance and low adhesion force with respect to the outer layer. Therefore, when such hose is used for inhalation and compression-transport of drainage or sludge in civil engineering works, the inner layer of the hose damages in an early stage.
It has been also proposed to form the inner layer in the flexible hose from a rubber material comprising an acrylonitrile-butadiene rubber (NBR) as a main component to insure thermal adhesive properties with respect to a soft synthetic resin (e.g., a soft poly(vinyl chloride)) forming the outer layer. The rubber material (NBR) forming an inner surface of such a hose has abrasion resistance to some extent, which surface directly contacts transported substances as inhaled and compression-transported. The abrasion resistance of the rubber material (NBR) is, however, limited. Therefore, the hose has a short product-life when it is used in applications in which the inner surface abrades severely. Accordingly, a hose having an extremely improved abrasion resistance has been desired. On the other hand, when the inner layer is composed of a rubber having high abrasion resistance, thermal adhesive properties of the inner layer with respect to a constitutive soft synthetic resin (e.g., a soft poly(vinyl chloride)) of the outer layer deteriorates, and the inner layer and outer layer hardly adhere to each other with high adhesive force to form a composite.